1. Field of the Invention
The present disclosure relates generally to Light-Emitting Diode (LED) lamps, and more particularly to integrated circuits for Alternating Current (AC) driven LED lamps and control methods thereof.
2. Description of the Prior Art
Light-Emitting Diodes or LEDs are increasingly being used for general lighting purposes. In one example, a set of LEDs is powered from an AC power source and the term “AC LED” is sometimes used to refer to such circuit. Concerns for AC LED include manufacture cost, power efficiency, power factor, flicker, lifespan, etc.
U.S. Pat. No. 9,374,863 demonstrates several AC LED lamps, and is incorporated by reference herein in its entirety. FIG. 1 duplicates an AC LED lamp 100 disclosed in U.S. Pat. No. 9,374,863, and could have the ability of eliminating a dark period that possibly appears when the AC power source is low in amplitude. AC LED lamp 100 could be flick-free.
In FIG. 1, an integrated circuit 102 has path switches SG1, SG2, SG3 and SG4, a path controller 24, and a bank controller 106. Each of path switches SG1, SG2, SG3 and SG4 provides a conduction path and connects one cathode of an LED group to a current source 25, which limits the maximum driving current from the LED string to the ground voltage. For example, the conduction path that the path switch SG1 controls connects the cathode of the LED group 201 and the current source 25. The path controller 24 is configured to adaptively control the path switches SG1, SG2, SG3 and SG4. For example, if the rectified input voltage VREC is so low that the current IG4 passing through the LED group 204 is about 0 A, then the path controller 24 turns on the path switch SG3, coupling the cathode of the LED group 203 directly to the current source 25.
A pulse generator 108 in FIG. 1 is configured to respond to signal S1 which the path controller 24 sends to control the path switch SG1, the most upstream path switch among all the path switches. When the signal S1 is asserted to turn on the path switch SG1, the pulse generator 108 is triggered to output a pulse SCONN with a predetermined pulse width. The pulse SCONN turns on the switch 116 such that the constant current source 118 conducts the control current ICTL from the base of the BJT 110. The pulse generator 108 determines the pulse width of the pulse SCONN, referred to as a connection period TCONN in this specification because the BJT 110 seemingly connects the capacitor 112 to the node REC when the pulse SCONN appears. The electric energy stored by the capacitor 112 in the power bank 104 could be released to power the LED groups 201, 202, 203 and 204 during the connection period TCONN, so as to keep some of the LED groups 201, 202, 203 and 204 illuminating when the input voltage VAC across an input port 16 is low in amplitude.